To use other peoples words as my own
In this sense it is loosely matched by the Latin phrase "memento mori" ("remember you have to die", which was whispered into the ear of victorious Roman generals during their parade of triumph, to remind them that all earthly success is fleeting.
Winter is coming, and now the dead are comming back alive to kill the living except now the dead can't speak and they possess blue eyes
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If you are unfamiliar with your old irish / welish / brittish history the story of Bran the Blessed, or put another way Bran of House Stark and his three eye crow is Bendigeidfran from one of the four stories told in the Mabinogi. (actually a more accurate description instead of "four stories" is "four branches"
Well the Mabinogi has a story of a holy grail that could bring back the dead for good or for evil (inspiration for the black cauldron) and the dead can be used for good or for evil. Bran the Blessed story deals with this tail.
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To steal another saying from A Song of Ice and Fire
Valar Morghulis is "all men must die" it is responded to by the saying "all men must serve."
Summer must always past in Autumn and eventually Winter. But the only way to survive the winter is to band together during the dark times until the plum blossoms bloom. The plum blossoms are trees that are relatives to the cherry blossoms. The difference between a plum blossom and a cherry blossom is that one flowers buds in winter and are proof that spring will eventually return (but the fruit of the tree comes later after winter has been chased away). A cherry blossom by contrast blooms in mid spring roughly april depending on the tree and where the tree is planted.
Or instead of a tree blossoming flowers, perhaps it is the cry of a wolf pup uniting the pack... a dire wolf cub whose name is Summer (Bran's wolf)